Foundry core binder and process for preparation thereof



United States Patent s 168 4% rouunnr Conn Brianna AND Pnocnss nonrnnrsnarron 'rrmnnor Lloyd H. Brown, Qrystal Lake, and David D. Watson,

Barrington, 111., assignors to The Quaker Guts Company, (Ihicago, Ill, acorporation of New Jersey No Drawing. Filed July 11, 1960, Ser. No.41,728 2 Claims. (Cl. 260-294) part of a metal casting. A foundry corebinder may be defined as that part of the foundry core which causesadhesion among the sand particles. To a large extent the properties of afoundry core are determined by the properties imparted to it by theparticular binder employed. There are certain required properties for afoundry core. It must resist the washing and burning action of a streamof hot metal; it must admit of the free escape of gases; it must impartits internal contour to the metal casting; it must have sutficienttensile strength so that it is not ruptured while being handled orworked; and finally it must collapse and shakeout after the metalcasting has hardened.

Various binders have been used in the foundries with varying degrees ofsuccess. One of the oldest known binders is the cereal-core oil binder.The main disadvantage of this system is the long curing time required.With the use of high speed automatic equipment a rapid curing binder isvery desirable.

Another type of core binder is made from phenolic resins. Because of thehigh cost of such resins, the binder is used to merely bond a shellinstead of acting as a binder throughout the core. The use of phenolicresin type binders results in cores that have a tendency to resistshakeout after the metal casting has hardened, especially with thecasting of low melting point non-ferrous alloys. Other disadvantages ofthe phenolic resin binders are extended curing times for the cores andless than satisfactory tensile strengths.

A third type of core binder is the urea-formaldehyde cereal binder. Thecore made from this binder collapses too readily on contact with hightemperature melting metals and loses strength in a high humidityatmosphere. In the preparation of this binder a solvent is required inorder to prevent crystallization or gelling. Water has been employed asthis solvent, but its use incurs certain undesirable elfects, such as anextended curing time and excessive shrinkage of the foundry core uponcuring. In addition, since the water is not a reactive solvent, it doesnot in any way improve any of the inherent weaknesses of theurea-formaldehyde resin.

It is an object of this invention to employ a reactive solvent in thepreparation of a urea-formaldehyde resin core binder which willsubstantially improve the properties of the urea-formaldehyde resin corebinder and in addition will not give the disadvantages of an aqueoussolvent. I

Another object of this invention is to produce a foundry sand binderthat imparts to the foundry core an improved tensile strength.

Still another object of this invention is to produce a binder that whenmixed with foundry sand cures rapidly so that the sand-binder mixturemay be used with highspeed automatic machinery.

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A further object of this invention is to produce a liquid foundry corebinder that when mixed with sand, cures at room temperature to form afoundry core which will produce a metal casting free from blowholesproduced by the gas evolution from the core.

A still further object of this invention is to produce a liquid binderthat gives a foundry core that can withstand the heat from a highmelting point metal and yet can be readily shaken out after the metalcasting has hardened.

Still another object of this invention is to produce a stable, liquidfoundry binder from materials that are relatively inexpensive ascompared to many presently used materials.

A further object of this invention is to produce a foundry core binderwhich gives foundry cores that do not lose strength in a high humidityatmosphere.

A still further object of this invention is to provide a liquid,resinous, foundry core binder that has sufficient stability for storageand shipment in commerce.

in accordance with the invention the above objects are accomplished by aprocess in which urea, furfuryl alcohol, and a non-polymerized aqueousmixture of formaldehyde, urea, and equilibrium reaction products thereofabout 15% by weight water. The resulting solution from the abovecomponents is adjusted to a pH in the range of 5.0 to 6.5; however, thepreferred range is a pH of 5.5 to 6.0. The said solution is thenrefluxed at to C. until the solution has a viscosity in the range of 350to 3000 centipoises if measured at 25 C. A preferred viscosity range forthis end point is 400 to 1500 centipoises. In the final step the pH ofthe solution is adjusted to a range 6.5 to 8.5.

Aqueous UP. mixtures (non-polymerized) are sold in commerce. One exampleis UP. Concentrate85. Another aqueous U.F. mixture is marketed asUrea-Formaldehyde 25-60. The formaldehyde, urea and equilibrium reactionproducts thereof, present in aqueous U.F. mixtures are believed to existin equilibria. as follows:

NH CONH HCHO:NH CONHCH OH NH CONHCH OH-l-HCHO :HOCH NHCONHCH OH HOCHNHcONHCl-l OH-l-HCHO :HOCH NHCON(CH OH) 2 HGCH NHCON CH OH) HCHO (HOCHNCON (CH OH) 2 The above equilibria illustrate What is meant by thephrase a non-polymerized aqueous mixture of formaldehyde, urea, andequilibrium reaction products thereof. Those urea molecules in theequilibria shown above that have more than one methylol radical attachedare sometimes referred to as polymethylol ureas. There is difficultyencountered in distinguishing between different polymethylol ureas inaqueous UJF. mixtures. .For this reason the composition of the aqueousU.F. solution is best reported in terms of the weight percent urea andformaldehyde. A typical analysis of aqueous U.F. mixture (U.F.Concentrate-85") shows 59% by weight form- 3 aldehyde, 26% by Weighturea, and at most by weight water.

The total amount of urea and formaldehyde present in the aforementionedsolution of this invention is stated in terms of a molar ratio. Theamount of urea added separately (as opposed to that urea included in theaqueous UJF. mixture) will vary with the analysis of the particularaqueous U.F. mixture that is employed. Thus the amount of urea to beadded separately can be determined from the aforementioned molar ratioand the analysis of the particular aqueous U15. mixture that isemployed.

The term available urea refers to free urea as well as urea combinedwith the methylol group in the equilibria shown above. The termavailable formaldehyde refers to free formaldehyde as well asformaldehyde combined with urea in the equilibria shown above.

The refluxing end point may be determined by either measuring therefractive index or by measuring the viscosity of the solution. However,measuring the viscosity is the preferred method to determine therefluxing end point. Both the refractive index and viscosity areindicators of the solutions stage of resinification. The stage ofresinification is critical because if there is not sufficientresinification the binder solution will be unstable. If the stage ofresinification becomes too advanced then the binder solutions highviscosity will prevent proper mixing of the binder with the sand at thefoundry.

The invention will be further illustrated but is not limited by thefollowing examples in which the quantities stated in parts are parts byweight unless otherwise indicated. When the percent of binder is stated,it is percent by weight based on the weight of the foundry sand. Whenthe percent of any of the components of the binder (e.g., furfurylalcohol, catalyst, water) are stated it is percent by weight based onthe total weight of the binder, unless otherwise indicated. All tensilestrengths are stated in pounds per square inch (p.s.i.).

Example 1 Into 2710 parts of UP. Concentrate-85 were admixed 2025 partsof furfuryl alcohol and 654 parts of urea. The pH of the resultingsolution was adjusted to 5.7 by the addition of 58% aqueous phosphoricacid. This solution was then charged into a 3-necked vessel equippedwith a stirrer, thermometer and reflux condenser. The solution washeated to 100 C. over a period of one hour, and then refluxed at aboutthat temperature for an additional two hours. The degree ofrcsinification was observed by checking the viscosity at regular timeintervals. When a withdrawn sample of the solution had a viscosity of380 centipoises at 25 C. as measured by a Brooklield viscometer, therefluxing was discontinued and 28 parts of sodium phosphate (in 125parts of water) were admixed to give a pH of 8.08. Upon cooling theresulting binder composition was a slightly cloudy, light-amber liquid.

Example 2 The procedure of Example 1 was repeated except that only 983parts furfuryl alcohol were admixed with the U.F. Concentrate-85, andthe pH of the solution was adjusted to 5.9 by the addition of 50%aqueous phosphoric acid. The progress of the resiniiication during therefluxing was observed by determining the time required for a sample ofthe hot solution to drain from a standard consistency cup with aorifice. When there was sixty second draining time, the refluxing Wasdiscontinned andthe solution was neutralized to a pH of 8 with 13 partsof NaOH in parts of water. Upon cooling the resulting binder compositionwas a slightly cloudy, light-amber liquid.

Example 3 To show the importance of the addition of furfuryl alcohol tothe aqueous UP. mixture, binders were prepared essentially as describedin Example 1 but with varying amounts of furfuryl alcohol. Foundry coreswere then produced employing these binders. To produce the foundrycores, the binders were mixed with sand and catalyst in the proportionsshown below and the resulting mixtures rammed into 1% x 2" core boxes.The resulting cores were removed from the core boxes and cured in anoven at 425 F. for 5 minutes. The cured cores were then placed in aDietert Thermolab Dilatometer at 1590 F. and 2500" F. for 5 minutes. Acompressive load was applied. I-lot strength at failure in pounds persquare inch was determined. The following results were obtained forthree cores employing 1.5% binder:

Percent Hot Strength Core Furfuryl Alcohol in Binder 1,500 F. 2,500 F.

The following results were obtained for three cores employing 2.0%binder:

Percent Hot Strength Core Furfuryl Alcohol in Binder 1,500 F. 2,500 F.

From the above results it is seen that the addition of furfuryl alcoholto the binder appreciably increases the hot strength.

Example 4 The procedure of Example 3 Was repeated except that the coreswere A" x 2 and were cured on a hot plate at 237 C. At specifiedintervals while on the hot plate the foundry cores were tapped lightlywith a spatula. The curing time was determined from the beginning of thebaking period to that time when an indentation was no longer made by thespatula. The following results were obtained. The term solids refers toall ingredients other than water in the binder before resinification.All percentages given are by weight and based on the binder.

Percent Cure Core Furfuryl Percent Percent Time Alcohol in SolidsCatalyst (seconds) Binder The above results show that if the solidscontent of the binder is lowered, a greater curing time is required.

Example 5 Percent Core Furfuryl Tensile Alcohol in Strength Binder H VE3 The following results were obtained for Thus the addition of furfurylalcohol to the core binder increases the tensile strength of the core.

Example 6 If there is excessive gas evolution from a foundry core Whilehot metal is being poured around the core, blow holes may result in themetal casting. To test for gas evolution the procedure of Example 3 wasessentially repeated except that the cores were cured at roomtemperature. The cores were crushed and ten gram samples of the crushedmaterial were placed in porcelain boats which were inserted in acombustion tube maintained at 1800 F. This test simulated the conditionsobtained when hot molten metal is poured around a foundry core. The gasevolved was collected in a burette at 120 C. over silicone oil. Thetotal volume of gas collected at 125 C. was measured in milliliters. Thepressure was equalized to atmospheric pressure. From cores made withbinders having 1.8% by weight solids (based on sand), 25% furfurylalcohol, and with varying percentages of water (percent by weight ofbinder) the following results were obtained:

Core Percent Volume Water of Gas The above results show considerablyless gas evolution for high solids binder (low water content) when thefoundry cores are cured at room temperature.

Example 7 Room temperature curing and oven curing are two separatemethods of curing foundry cores. Oven curing is desirable for some usesbecause the foundry cores moisture content is lowered during theheating. Foundry 0 fromthis invention. The procedure for determining gasevolution from the foundry cores was repeated as in Example 6. The totalvolume of gas (in milliliters and percent collected at 120 C.) evolvedwas measured at succes- Core mx Tensile sive time intervals from thetime the core was initially Alcohol in Strength a Bi exposed to the 1800F. temperature. The results were as follows:

r Time (Minutes) Core 1 Core 2 Core 3 The following results wereobtained for 3 cores employg9 33 i 162 110 95 Hg 3% bmder 163 115 100172 gs 198 Percent 176 0 5 Core Furturyl Tensile Algcpigfm Strength 187142 132 7 0 350 The tensile strength of core 1 was only 300 p.s.i.;while 2 e 258 90 cores 2 and 3 had a tensile strength of 500 p.s.i. To

raise the tensile strength of core 1 to the level of the cores 2 and 3would require an inrcease in the percent of binder. Since the amount ofgas evolved is directly proportional to the amount of binder employed inthe core, core 1 would evolve an even greater volume of gas ifsufiicient additional binder were employed to give a tensile strengthequivalent to that of cores 2 and 3. The amount of gas evolved duringthe first few minutes of exposure to the molten metal is especiallycritical. During the first few minutes of exposure before there has beenan appre ciable amount of solidification of the molten metal, the gasevolved can cause more blowhole damage, than later evolved gas. Thesuperiority of the cores produced by the binders of this invention isapparent from the aboveresults which show that there is considerablyless gas evolution from cores produced by the binders of this invention,particularly during the first few minutes of heat exposure.

We claim: v

1. A process for the preparation of a stable, liquid,

resinous, foundry core binder comprising the steps of,

(a) forming a solution from an aqueous mixture of formaldehyde, urea andmethylol ureas, said aqueous mixture containing at most about by weightof water; and furfuryl alcohol; the molar ratio of total available ureato available formaldehyde in said solution being in the range of about1:1.75 to 1:30, said furfuryl alcohol being present in said solution insuch amount that it constitutes about 15 to by weight of said solution;

(b) adjusting said solution to a pH in the range of about 5.0 to 6.5;

(c) then refluxing the adjusted solution at about to C. until theadjusted solution has a viscosity in the range of about 350 to 3000centipoises if measured at 25 C.; and

(d) then adjusting the refluxed solution to a pH in the range of about6.5 to 8.5.

2. A foundry core binder prepared according to the process of claim 1.

FOREIGN PATENTS Canada Aug. 14, 1956

1. A PROCESS FOR THE PREPARATION OF A STABLE, LIQUID, RESINOUS, FOUNDRYCORE BINDER COMPRISING THE STEPS OF, (A) FORMING A SOLUTION FROM ANAQUEOUS MIXTURE OF FORMALDEHYDE, UREA AND METHYOL UREAS, SAID AQUEOUSMIXTURE CONTAINING AT MOST ABOUT 15% BY WEIGHT OF WATER; AND FURFURYLALCOHOL; THE MOLAR RATIO OF TOTAL AVAILABLE UREA TO AVAILABLEFORMALDEHYDE IN SAID SOLUTION BEING IN THE RANGE OF ABOUT 1:1.75 TO1:3.0, SAID FURFURYL ALCOHOL BEING PRESENT IN SAID SOLUTION IN SUCHAMOUNT THAT IT CONSTITUTES ABOUT 15 TO 50% BY WEIGHT OF SAID SOLUTION;(B) ADJUSTING SAID SOLUTION TO A PH IN THE RANGE OF ABOUT 5.0 TO 6.5;(C) THEN REFLUXING THE ADJUSTED SOLUTON AT ABOUT 95* TO 105*C. UNTIL THEADJUSTED SOLUTION HAS A VISCOSITY IN THE RANGE OF ABOUT 350 TO 3000CENTIPOISES IF MEASURED AT 25*C.; AND (D) THEN ADJUSTING THE REFLUXEDSOLUTION TO A PH IN THE RANGE OF ABOUT 6.5 TO 8.5.